A company pays its trainee engineer a stipend that increases by a fixed amount every month. In the first month the stipend is ₹12,000 and in the second month it is ₹12,800.
(i) Obtain an expression for the stipend in the nth month.
(ii) Calculate the stipend for the 15th month.
(iii) In which month will the stipend first exceed ₹20,000?